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<a name="H8_002f300"></a>
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<a name="ld-and-the-H8_002f300"></a>
<h3 class="section">4.1 <code>ld</code> and the H8/300</h3>

<a name="index-H8_002f300-support"></a>
<p>For the H8/300, <code>ld</code> can perform these global optimizations when
you specify the &lsquo;<samp>--relax</samp>&rsquo; command-line option.
</p>
<dl compact="compact">
<dd><a name="index-relaxing-on-H8_002f300"></a>
</dd>
<dt><em>relaxing address modes</em></dt>
<dd><p><code>ld</code> finds all <code>jsr</code> and <code>jmp</code> instructions whose
targets are within eight bits, and turns them into eight-bit
program-counter relative <code>bsr</code> and <code>bra</code> instructions,
respectively.
</p>
<a name="index-synthesizing-on-H8_002f300"></a>
</dd>
<dt><em>synthesizing instructions</em></dt>
<dd><p><code>ld</code> finds all <code>mov.b</code> instructions which use the
sixteen-bit absolute address form, but refer to the top
page of memory, and changes them to use the eight-bit address form.
(That is: the linker turns &lsquo;<samp>mov.b <code>@</code><var>aa</var>:16</samp>&rsquo; into
&lsquo;<samp>mov.b <code>@</code><var>aa</var>:8</samp>&rsquo; whenever the address <var>aa</var> is in the
top page of memory).
</p>
<p><code>ld</code> finds all <code>mov</code> instructions which use the register
indirect with 32-bit displacement addressing mode, but use a small
displacement inside 16-bit displacement range, and changes them to use
the 16-bit displacement form.  (That is: the linker turns &lsquo;<samp>mov.b
<code>@</code><var>d</var>:32,ERx</samp>&rsquo; into &lsquo;<samp>mov.b <code>@</code><var>d</var>:16,ERx</samp>&rsquo;
whenever the displacement <var>d</var> is in the 16 bit signed integer
range. Only implemented in ELF-format ld).
</p>
</dd>
<dt><em>bit manipulation instructions</em></dt>
<dd><p><code>ld</code> finds all bit manipulation instructions like <code>band, bclr,
biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor</code>
which use 32 bit and 16 bit absolute address form, but refer to the top
page of memory, and changes them to use the 8 bit address form.
(That is: the linker turns &lsquo;<samp>bset #xx:3,<code>@</code><var>aa</var>:32</samp>&rsquo; into
&lsquo;<samp>bset #xx:3,<code>@</code><var>aa</var>:8</samp>&rsquo; whenever the address <var>aa</var> is in
the top page of memory).
</p>
</dd>
<dt><em>system control instructions</em></dt>
<dd><p><code>ld</code> finds all <code>ldc.w, stc.w</code> instructions which use the
32 bit absolute address form, but refer to the top page of memory, and
changes them to use 16 bit address form.
(That is: the linker turns &lsquo;<samp>ldc.w <code>@</code><var>aa</var>:32,ccr</samp>&rsquo; into
&lsquo;<samp>ldc.w <code>@</code><var>aa</var>:16,ccr</samp>&rsquo; whenever the address <var>aa</var> is in
the top page of memory).
</p></dd>
</dl>




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